Only show one error message for an invalid email

If notification_email is blank, it's set from email. If an admin
attempted to create a user with an invalid email, an error would be
displayed for both fields. Only validate the notification_email if it's
different from email.

app/models/user.rb

@@ -93,8 +93,10 @@ class User < ActiveRecord::Base
   #
   # Validations
   #
+  # Note: devise :validatable above adds validations for :email and :password
   validates :name, presence: true
-  validates :notification_email, presence: true, email: true
+  validates :notification_email, presence: true
+  validates :notification_email, email: true, if: ->(user) { user.notification_email != user.email }
   validates :public_email, presence: true, uniqueness: true, email: true, allow_blank: true
   validates :bio, length: { maximum: 255 }, allow_blank: true
   validates :projects_limit, presence: true, numericality: { greater_than_or_equal_to: 0 }

spec/controllers/admin/users_controller_spec.rb

@@ -114,6 +114,17 @@ describe Admin::UsersController do
     end
   end
 
+  describe 'POST create' do
+    it 'creates the user' do
+      expect{ post :create, user: attributes_for(:user) }.to change{ User.count }.by(1)
+    end
+
+    it 'shows only one error message for an invalid email' do
+      post :create, user: attributes_for(:user, email: 'bogus')
+      expect(assigns[:user].errors).to contain_exactly("Email is invalid")
+    end
+  end
+
   describe 'POST update' do
     context 'when the password has changed' do
       def update_password(user, password, password_confirmation = nil)